The present invention relates to interferometers constructed on the basis of the Michelson interferometer principle. The Michelson interferometer generally comprises a monochromatic radiation source, an optical beam splitting means such as a semitransparent plate, which supplies two measuring arms terminated by mirrors and a radiation detector arranged so as to collect in superimposed manner via the optical splitting means the radiation which has performed an outward and return movement along the two measuring arms. Such a device makes it possible to measure a large number of physical quantities able to affect the propagation of optical radiation along the measuring arms. Certain of these physical quantities cause reciprocal effects which produce the same transmission delay whatever the propagation direction of the optical radiation in each of the measuring arms. Other physical quantities lead to non-reciprocal effects which influence the transmission delay in a different manner as a function of the propagation direction of the optical radiation. The usually considered non-reciprocal effects are the Faraday effect and the relativistic inertial effect. The Faraday effect occurs when the measuring arm comprises a material medium in which a magnetic field creates a preferred electron spin orientation. The use of this effect has made it possible to adapt the interferometer to the measurement of electric currents. In this case the measuring arms can be looped by circulating the optical radiation in a waveguide, such as an optical fibre excited at each end. This makes it possible to eliminate the mirrors and the interferometer becomes an annular interferometer. The relativistic inertial effect used in an annular interferometer is called the Sagnac effect and the interferometer is then called a gyrometer.
The reciprocal effects are not linked with the destruction of the symmetry of the space or a material medium. They are observed when the measuring arms are the sources of mechanical, optical or thermal stresses.
When a Michelson interferometer is used for measuring a particular physical quantity, it is generally sensitive to other physical quantities which may falsify the measurement.
In the case of a reciprocal effect, the mirrors conventionally fitted at the end of the measuring arms make the latter appear twice as long as they are in reality, which is a major disadvantage on wishing to measure a nonreciprocal effect.
In addition, optical reflector systems are known, which are based on the use of photorefractive media making it possible to reflect an incident wave front in the form of a conjugate wave front. An ordinary mirror reflects the light as if it came from a virtual object not coinciding with the object illuminating the mirror. However, a photorefractive medium can reflect a wave front having a conjugate phase, which returns to the object radiation isomorphic of that which came therefrom. In the case of reciprocal effects, this interactive reflection ensures the insensitivity to such effects, provided that they have not varied during the outward and return passage of the radiation and the photorefractive medium has been able to adapt to the variations of these effects. However, this ability to cancel out the reciprocal effects is not prejudicial to the interferometric measurement of the non-reciprocal effects, which provides new possibilities for the use of the Michelson interferometer in a field conventionally reserved for the annular interferometer.